Image correlator tube with crossed field deflection

ABSTRACT

A device of the image orthicon type is disclosed for electrooptical integration and correlation systems utilizing a crossed electric and magnetic field deflection region and a retarding potential filter. The crossed electric and magnetic fields deflect a beam of primary electrons from a photoemissive cathode for the conversion of collimated light input signals within the electron image section which results in the emission of secondary electrons impinging on a target member. The retarding potential filter is biased at a potential to optimize the effective secondary electron emission ratio relative to the primary photoelectrons.

United States Patent 11 1 1111 3,748,524

Osepchuk July 24, 1973 IMAGE CORRELATOR TUBE WITH 3,388,282 6/1968 Hankin et a1. 315/11 x CROSSED FIELD DEFLECTION 3,409,791 11/1968 Ahizaki et a1... 313/76 3,491,262 1/1970 Olsson 315/10 [75] Inventor: John M. Osepchuk, Concord, Mass. [73] Assignee: Raytheon Company, Lexington, 'f' Emmi"e"-Carl Quarfbnh Mass Assistant Examiner-J. A. Nelson Attmey-Harold A. Murphy, Joseph D. Pannone and [22] F11ed: Sept. 14, 1970 Edgar Rest [21} Appl. No.: 71,956

[57] ABSTRACT [52] U s Cl 315/11 315/12 313/75 A device of the image orthicon type is disclosed for 340/ MP electrooptical integration and correlation systems l ti- 51 rm. c1. H01j 31/48 "1 a and mignenc field deflect 53 Field of Search 315/ 11 12 and a retard filter The 313/ 76 83, 346/3 k electric and magnetic fields deflect a beam of primary electrons from a photoemissive cathode for the conver- 1561 1122;221:33513221115521221121231255521" UNITED STATES PATENTS ary electrons impinging on a target member. The re- 3,654,596 4/1972 Osepchuk 315/11 X ta -din potential filter is biased at a, potential to opti- 2,97s,44s 2/1961 Rogers.....

315/10 X mize the effective secondary electron emission ratio 3,134,926 5 1964 H d 315 10 3 225 271 12/1965 KZLSJZeR et a]. 313/76 x relat've the pnmary photoelectmns' 3,243,643 3/1966 Toohig 315/11 UX 2 Claims, 12 Drawing Figures (60 .SIGNAL F" T INPUT N0 1 94 as j 10310531.... 80 82 a? 92 1 I I I I a2 "96 l j 70 V a cnosseo i 68 1 /00 FIELD OUTPUT 1 f DEFLECTION r M o 54 SIGNAL SYSTEM j 9 1 I 1 7a 1 1 7s as J6/ZI/E k \r f v vv v vw i 62 +V Emmi/1L INPUT NO. 2 v0) ELECTRON MULTIPLIER AND SCAN SECTION 4 RETARDING @POTENTIAL FILTER TARGET ENVELOPE SHEET 1 BF 4 $OLENOID ELECTRON IMAGE SECTION- N m T am. my EY i PATENTEU ENERGY OF PRIMARY ELECTRON S INCIDENT ON TARGET PATENIEI] JUL 2 4 I975 SHEET 3 0F 4 g /02 l SCAN BEAM SCAN BEAM TO COLLECTOR SIGNAL OUT SOLENOID @RETARDING DYNODE POTENTIAL FILTER SECONDARY BEAM {n SCAN CYCLE SCAN BEAM //3a /O--+M--{|I CORRELATION CYCLE PATENYED JUL 2 4 I975 SHEH HIF4 I l l l l I l I l I l l R f O NM T 6 AAR CEL x 88m 6 C 3 Y R 0% 4 M W TO 0 D O H qmd N T E HT Bl O PA UX ym-L C TA EEO S C NM Ma G F l l I l l I l I l I I l l l||| SCAN BEAM /46 CORRELATION A CYCLE sc'AN CYCLE M ETA LIZED COLLECTOR IMAGE CORRELATOR TUBE WITH CROSSEID FIELD DEFLECTION BACKGROUND OF THE INVENTION l. Field of the Invention The invention relates to electrooptical correlation systems and electron discharge devices for conversion and translation of multiple electrical signals utilizing crossed electric and magnetic field producing means.

2. Description of the Prior Art In the communications art the employment of electrooptical techniques in the processing of information results in a mixture of input signals from which are extracted only those integrated signals which correspond to a chosen time sequence pattern. The output comprises a signal varying in time in accordance with a modulated electrical pattern which may be coupled to any utilization load. Electrooptical correlator devices, particularly electron discharge devices of the image orthicon type are desirable in the processing of information to obtain high resolution in target definition and location. For the purposes of this specification the term correlation" shall be interpreted to refer to the multiplication of two functions in the processing of intelligence signals plus the integration and readout by electrical means of the signal waveforms. An area for the utilization of such devices resides in aerial observation and mapping utilizing high frequency electromagnetic energy waves to provide instant optical outputs without assimilating the data at a later time.

In a system utilizing electrooptical correlation techniques energy signals are modulated by elastic waves within a solid state material to provide collimated light waves. Such waves are electrically multiplied by a second input electrical signal which provides a bidimensional replica of the initial transmitted signal. The resultant product evolved by the correlation process is a real time variable electrical signal which may be periodically translated in a TV raster manner to be recorded ordisplayed on a monitor. An electrical conversion and translation device of interest is the image orthicon tube having the essential components for electrooptical correlation. A photoemissive cathode disposed within an evacuated envelope converts the incident collimated image rays into an electron discharge image by means of primary and secondary electron emission. An electron lens system processes these signals by impingement on an insulated dielectric target member for integration and correlation. An electron gun and deflection system scanning the accumulated charge potential stored on the target is disposed on the reverse side in an electron multiplier and readout section to yield a correlated signal output. The primary problem in utilizing such devices resides in the means for inserting the second input electrical required for the correlation techniques and the mode of operating the dielectric target member.

Prior art attempts to adapt electron discharge devices of the image orthicon type to perform the correlation and integration functions have suggested the operation of the target member close to its critical voltage or first crossover" operating mode to reduce the charge distributions produced by uncorrelated signals. Operation at this critical voltage is nonlinear and unstable and, therefore, attempts to utilize image correlation techniques in this area have been relatively unsuccessful. Operation at extremely high voltages or the second crossover operating mode results in the accumulation of positive charges from uncorrelated signals building up on the dielectric target member which drastically reduces the usable dynamic range and requires periodic discharging cycles by the scanning beam. In addition, modulation of the electron beam velocity produces drastic disturbances of the electron optical system focus.

A suggestion for achieving high uniformity and stability, as well as a high degree oflinearity of the secondary emission characteristics involves the utilization of the intermediate crossover operating modes. The input electrical correlation signal is injected on one or more of the electrodes within the electron image section of the overall device. In United States Letters Patent No. 3,474,286 issued to Rudolph C. l-lergenrother, on October 21, 1969, the photoelectric emission current from the photocathode is modulated by an adjacent mesh electrode to which the second input electric correlation signal is applied. Operation in the intermediate crossover mode results in substantially the same voltages being applied to the electrodes as would be used in the operation of an image orthicon device as a television camera tube. Numerous other prior art embodiments have utilized additional mesh members disposed either anteriorly or posteriorly with relation to the dielectric target member to control the potential on the target member surface.

In a copending application for United States Letters Patent entitled Image Correlator Tube, filed by John M. Osepchuk, Ser. No. 65874, filed Aug. 21, 1970, an interesting approach is advanced to provide a multiplication factor within the electron image section by an intermediately disposed dynode electrode member of an electron conductive dielectric material. The dynode electrode provides for the direct generation of a large number of secondary electrons by the transmission of primary photoelectrons through such electrode. The secondary electron emission is a linear function of the primary photoelectron energy and the low density transmission material provides uniform yields without the instabilities found in prior art secondary electron emissive surfaces involving the reflection process for emission.

A large part of the observed deviations in performance of prior art embodiments is believed to result from space charge effects, target surface contamination, as well as transverse leakage or field effects. A need arises, therefore, for superior means for introducing modulation of photoelectric emission current in de vices to be utilized in electrooptical correlation systems. The modulation desired should produce both positive and negative charge effects on the target member and operate in the relatively stable intermediate crossover region.

SUMMARY OF THE INVENTION In accordance with the teachings of the present invention a photoelectric emission current is provided within an electron image section of a device similar to the image orthicon tube. A crossed electric and magnetic focusing field deflects the primary photoelectrons and directs them to impinge upon a dielectric target member releasing secondary electrons. A retarding potential filter biased at a potential to optimize the secondary electron emission ratio houses the target member which may be scanned on the reverse side by a conventional electron scan beam and multiplier arrangement. The reflected secondary electrons are redirected through the crossed field region and deflected to be collected by a suitable electrical means. Mesh screen members for biasing the target member in the path of the secondary electrons are now eliminated to reduce some of the prior art disadvantages. By means of the crossed field region it is possible to provide for the viewing of the electron image output on the same side as the impinging light rays on the photoemissive cathode.

Alternately, in one embodiment of the invention a dynode target member of a material similar to that discussed in the aforereferenced pending patent application by John M. Osepchuk is utilized. This electrode member is positioned in the path of the photoelectric emission current to provide a multiplication factor of the photoelectrons transmitted through the member to yield a profusion of secondary electrons. The reflected electrical signals are collected by electrodes and translation means such as an electron scan beam and multiplier arrangement to derive a correlated electrical output signal.

The second input electrical correlation signals are provided in the electrooptical correlation system by applying a modulation voltage to the retarding potential filter. Alternately, in embodiments with the dynode target themodulation may be applied to the photocathode or target and retarding potential filter together. The utilization of the dynode target material provides a higher yield in the secondary electron emission ratio to assist operation in the intermediate crossover operating mode. In numerous instances the structure disclosed in the present invention permits latitude in the utilization of the output signals by either direct readout utilizing a conventional image orthicon scanning and mutliplier structure or direct viewing on a suitable vidicon monitor disposed along the same plane as the photocathode upon which the initial energy rays impinge.

BRIEF DESCRIPTION OF THE DRAWINGS I The invention, as well as the details for the provision of the preferred embodiments, will be readily understood after consideration of the following detailed description and reference to the accompanying drawings, wherein:

FIG. 1 is a detailed diagrammatic view of the illustrative embodiment of the invention;

FIG. 2 is a cross-sectional view of a crossed field deflection arrangement for utilization in the illustrative embodiment of the invention oriented along the line 2-2 in FIG. I;

FIG. 3 is a detailed diagrammatic view of an electrooptical correlation system embodiment of the invention;

FIG. 4 is a graph illustrative of the secondary elec+ tron emission ratio characteristics utilized in the illustrative embodiment;

FIG. 5 is a schematic diagram of the rear scan arrangement for signal translation;

FIG. 6 is a schematic diagram illustrative of an arrangement for signal translation on the image side of the illustrative embodiment; I

FIG. 7 is a diagrammatic illustration of the location of the initial energy impinging means and translation means oriented along a similar side;

FIG. 8 is a detailed diagrammatic view of an alternative embodiment of the invention;

FIG. 9 is a schematic diagram for signal translation utilizing two rear target meshes and a readout beam;

FIG. 10 is a schematic diagram of signal translation means utilizing a single rear target mesh and a readout beam;

FIG. 11 is a schematic diagram illustrative of a splittype photocathode; and

FIG. 12 is a cross-sectional view of horizontal and vertical crossed field deflection structure for utilization in the illustrative embodiment for signal translation on the image side.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings FIG. 1 illustrates the embodiment of the invention with the electron image section 2 followed by a multiplier and scanning section 4 all housed within envelope 6 illustrated diagrammatically by the dotted line. For the sake of clarity the details with regard to the construction of the multiplier and scan section have been described and illustrated in connection with FIG. 3 in order to specifically highlight the significant features of the invention. Magnetic field producing means 8, such as a solenoid, surrounds the device to provide a uniform magnetic field B oriented parallel to the axis of the device as indicated by the arrow 10.

Before proceeding with the detailed description of the illustrative embodiment in FIG. 1, a discussion of the conventional secondary electron emission ratio characteristics will be of assistance. FIG. 4 illustrates the relationship of the secondary electron emission ratio to the energy of the striking primary photoelectrons. The term secondary electron emission ratio is derived by dividing the current of the secondary electron emission by the primary electron current. The profile depicted by curve 12 represents the region between a sensitized surface of primary photoelectrons such as a photocathode indicated by line 14 and a target source of secondary electrons. In order to conform to the operational requirement for the secondary emission ratio to have a value of unity or greater, the minimum point for successful operation of an electron discharge device of the type under consideration would be the point indicated by the dashed line 16. It will be noted that curve 12 has an intrinsic dip at point 18 which is well below unity in the region close to the photocathode surface. The point in the operation mode where the secondary emission ratio is unity is referred to in the art as the crossover potential. In the illustration, then, the first crossover point is approximately 20 volts. Attempts to operate image correlator tubes at this voltage have raised problems with the distribution of the charge on the target member resulting in unstable operation and lack of uniformity of target definition. A high yield is noted at approximately 400 volts indicated by dashed line 20 followed by crossover point 24. This region will be referred to as the intermediate crossover operating mode.

Another crossover point noted in the art is indicated by the dashed line 22 for energy levels of approximately 5,000 volts. Such high voltages, however, have not yielded practical embodiments and have presented problems in stability, as well as sensitivity. The intermediate crossover mode region, therefore,.has been found to provide the most effective secondary electron emission ratio to lead to stable operation of the image correlator device. The target member upon which the primary electrons impinge to release the secondary electrons, therefore, will exhibit superior linearity, as well as stability, when operated at a few volts positive or negative with respect to point 24.

In accordance with the invention as illustrated in FIGS. 1 and 2 the electron image section 2 of the overall device incorporates a photocathode 26 biased at potential V,, having a photosensitized surface capable of emitting primary photoelectrons. The photoelectrons are focused by magnetic field producing means 8, as well as electrical focusing means such as drift tube 28. In addition, accelerating and deflection plates 30 and 32 may be provided together with accelerating means 34 all at ground potential. The secondary electrons emanating from the target are collected by collector 36.

It will assist in an understanding of the invention to clarify the usage of certain terms with regard to the applied voltage potentials. The term -V,, will refer to the cathode potential. The term V, will relate to the electron beam potential, +V is collector potential, and V,, the anode potential. All the potentials are indicated with respect to ground potential.

A crossed field deflection system 37 is provided to laterally displace and separate the primary and secondary electron beams. This will avoid some prior art disadvantages where reciprocal movement of such primary and secondary electrons exists within the electron image section 2. The separation of the primary and secondary electrons results in enhancement of operation in the intermediate crossover operating mode and insures that substantially all secondary electrons do not interfere with and reduce primary electron energy. The separation of primaries and secondaries will also result in the complete collection of the secondaries by a collector electrode and dispense with all target mesh members which at best are imperfect collectors.

Referring to FIG. 2 an illustrative embodiment of the crossed field deflection system 37 is shown. Opposing conductive plate members 38 and 40 with a spacing and length of, illustratively, a few centimeters, having bowed surfaces 41 and 42 provide a transverse electric field which together with the magnetic field define integrated adiabatic electric-rnagnetic field motion. Plate member 38 is biased at a positive potential indicated +V while the opposing plate member 40 is biased at a negative potential V, with a differential, illustratively, of a few hundred volts and a magnetic field of, illustratively, a few hundred gauss. The combined fields, then, will react on the beam of primary photoelectrons 44 to orient such electrons substantially along the central axis of the device as indicated by the dashed line 46. With the electric field potentials represented by the vector X and the magnetic field by the vector Z the beam will move substantially laterally or in the Y direction orthogonal to the first two vectors. Ideally, by adiabatic crossed field theory if the change in the E field experienced by the electron beam during one cycloid is small enough, then the transverse motional energy remains substantially invariant and no deterioration of the electron beam optics resultsbecause of any amplified beam trajectories in the transverse plane.

After deflection the beam of primary photoelectrons impinges upon the surface of target member 48. This member maybe fabricated of the well known combination of dielectric or electron transparent materials together with a conductive backing 52 or be provided without a conductive layer. The target member is also biased at ground potential and is electrically isolated from the cylindrical drift tube 28 by insulating means 54.

A retarding potential filter 56 is defined in the region between the target member and the crossed field deflection system and is isolated by insulator means 58 from the target member 50 and drift tube 28. This filter provides for the selective transmission of the desired electron secondaries and is provided with a negative bias at a value for which the effective secondary emission ratio of the target member 48 is unity at, for example, the desired intermediate crossover operating mode. The retarding potential filter is supperior to mesh members adjacent the target surface because there are no transparency problems or incidental secondary electron emission which has plagued prior art electron discharge devices when used for image correlation. To assist in minimizing shading of the electron images due to transverse electric fields the retarding potential filter member 56 may preferably have a diameter value substantially larger, for example, by a factor of two, relative to the target member dimensions. Voltage biasing supply 60 is utilized for the application of the desired negative bias in the range of, illustratively,

10 to 50 volts depending on the diameter and length of filter 56 as taught on pages 187-189 of the text Electron Optics by O. Klemperer, Cambridge, England, 1939, discussing, particularly, the Einzel lens and the equipotential planes across the filter.. Further, in accordance with the teachings of the present invention the secondary electron beam ratio is modulated in accordance with the signals inductively coupled from a suitable source 62 to provide the second input electrical correlating signal denoted by the symbol V(t). Such signals provide a replica of the time varying signals which are combined with the optically delayed collimated signals in the correlation and integration process employed in the electrooptical correlation systems hereinafter to be described. The returning secondaries along the path indicated by the dashed line 46 are deflected and separated in the same manner as the primary electron beam as indicated by the dashed line 62 to impinge upon the collector 36. The crossed field deflection system 37 coupled with the retarding potential filter 56 which may be utilized as a signal modulating means permits substantially complete separation of the primary and secondary electrons together with the substantial collection of all secondaries to measurably reduce the beam focusing aberrations which have heretofore plagued prior art image correlator devices. A dis cussion of crossed field deflection systems of the type utilized in the present invention is found in the article Method of Measuring the Normal Velocity Distribution of Secondary Electrons at Low Primary Bombarding Energy by V. Evtuhov, G. F. Smith and L. S. Yaggy in the Review of Scientific instruments, Volume 32, No. 12, Dec. 1961, Pages 13624366. Additionally, articles by Rose & lams, RCA Review 4 186 (1939) and Proceedings [RE 27 (547) (1939) provide excellent discussions ofthe operation of crossed field deflection devices.

in one embodiment of the invention target member 48 may be scanned with the conventional scan beam means contained within section 4 as shown in FIG. 3.

A low velocity electron scanning beam 64 emanates from the cathode 66 of gun assembly 68 which is biased along with an internal conductive focusing means 70 by voltage supply 72. The impingement of the photoelectrons on the electron image side of the target member 48 results in a deposition of a positive charge of a few volts. The scanning beam 64 deposits negative electrons in the areas corresponding to the positively charged image areas. A returning electron beam 74 contacts anode member 76 of the gun assembly 68 to be scattered, deflected and collected by a plurality of conventional dynode electrodes together with collecting electrodes for generating a correlated output signal coupled by means of lead 78 to an external utilization load. The conversion and translation of both the positive and negative electron image signals together with the modulation introduced by the retarding potential filter provides a time varying signal replica for the electrooptical correlator system in which the device under consideration is employed. The positive charges deposited on the target member 48 require a greater number of electrons during the scanning cycle for neutralizing such charges. These portions of the target member indicate the initially more intensely illuminated areas of the initial image and require a substantially greater number of electrons than the darker areas under examination. As a result, in'returning scan beam 74 modulation in the correlated electrical signal output will be the difference between the initial scan beam and the current extracted in the neutralizing process to result in a net negative signal representing a correlated electromagnetic image. The external deflection, as well as alignment magnetic means, are indicated generally by the numeral 80 for provision of the desired deflection and scanning of the scan beam in this section.

FIG. 3 is also illustrative of the image correlator device of the present invention in an electrooptical correlation system. Electromagnetic energy originating from a source 82 is directed by means of lens 84 to form a collimated beam of, for example, light rays 86 passing through a solid state modulator 88. The beam is first focused through a polarizer 90 upon a material capable of supporting elastic waves, such as quartz, upon stimulation by electrical input signals applied'to transducer 92 from terminal 94. The transducer is of the piezoelectric type and provides for the application of the first input electrical correlation signal to the delay line 96 of the optical modulator with the opposing end terminated in an energy absorber 98 to prevent the backward wave reflection.

A second light polarizer 100 follows the modulator 88 and the emergent modulated beam impinges upon the photosensitive cathode 26 of the electron image section 2 which provides the electrical conversion and translating means with the subsequent section 4 providing the multiplication, integration and correlation functions for the overall system.

FIG. is illustrative of a scan beam on the target member 48 with a rear target mesh 102 which may be utilized to enhance the readout or even provide for introduction of modulating signals in an electrooptical correlation system.

FIGS. 6 and 7 illustrate another capability of the structure of the present invention in the provision of the target scan on the same side as the original impinging electron image on the photocathode 26. In this embodiment a scan beam gun, as well as the beam collector, will be oriented coplanar and coaxial with respect to the tube axis 104 within envelope 6. The scan beam gun assembly 106 is collected by means of collector 108 while the secondary electron beam directed by means of the retarding potential filter and crossed field deflection system impinges on the collector 36 as in FIG. 1. In this embodiment the scan beam is indicated by the numeral 110 while the output signal is obtained in the beam collector current indicated by the numeral 112. Target member 48 will not require a backing of a conductive material and the deflection system for this embodiment will be described withreference being directed to FIG. 12. Deflecting plate members 38 and 40 provide an adiabatic composite field motion and the electric field potentials are indicated by the solid lines 114. The primary photoelectron beam from the photocathode 26 is deflected by the set of plate members 38 and 40 oriented in the vertical manner. Similarly, the returning reflected secondaries will be deflected to the collector 36 utilizing the same plate members 38 and 40. During the scan cycle another set of deflecting plate members 116 and 118 will be operated in order that the vertically disposed plate members will provide a slow vertical sweep while the remaining set of plate members 116 and 118 yield a fast horizontal sweep. During the electron image recording cycle the horizontal plate members will have no potential supplied. This illustrative means for scanning of the electron image signals will be equally applicable to other embodiments of the invention described herein.

In the embodiment shown in FIG. 8 the multiplication capabilities in the emission of secondary electrons utilizing electron conductive materials as described in the aforereferenced pending patent application may be employed in conjunction with the crossed field deflection system and retarding potential filter to introduce further efficiencies, as well as modulation means for the second input electrical correlation signals. In this embodiment structure similar to that previously described has been designated by similar reference numerals. The superior linear modulation characteristics and multiplication factors in the range of three to four times higher than conventional secondary electron emission targets is utilized for the target member 122. Numerous examples of the electron conductive dielectric material have been suggested in the art for target members of the disclosed type which releases a profusion of secondary electrons rather than relying upon reflection impinging primary electrons rather than relying upon reflection for the emission of such secondaries. Potassium chloride or any of the halides may be deposited on a substrate of a metal, such as aluminum, to-

gether with an impinging surface of aluminum oxide. Various other thin film targets will be readily available to those skilled in the art including magnesium oxide and thicknesses of 10 to 12 microns will provide the desired secondary electron emission ratio levels. In accordance with the aforereferenced patent application the material potassium chloride can provide a secondary electron yield varying from a ratio of 16 to as high as 40 with the collecting voltages varied from between 50 volts to 250 volts.

The target member 122 of the electron conductive material having multiplication potentials is supported within the envelope in front of the retarding potential filter 56 and is electrically isolated from the drift tube 28 by similar insulating means 54 and 56. In view of the high multiplication factor of the target member the term dynode" will be utilized to refer to this structure. The dynode target member 122 is biased at ground potential. To assist in the emission of the transmitted secondary electrons which are returned through the target member by the retarding potential filter a second collector electrode 124 is mounted in the path aligned with the dynode target member 122. A suitable biasing V62. The retarding potential filter 56 is biased by a variable negative voltage supply and is electrically insulated from the dynode target collector 124 by insulators 128.

This embodiment provides for a crossed field deflection system 37 which deflects the image on the photocathode 26 before it proceeds to the dynode target member 122. The retarding potential filter 56 is again biased negatively so that the total effective secondary emission ratio is unity for effective operation in the intermediate crossover operating mode. In this embodiment, however, a new capability is introduced for the introduction of the modulation signal V(t). In place of modulation of the retarding potential filter as in FIG. 1 the second input electrical correlation signal is now introduced directly on the photocathode 26 which is biased negatively by voltage supply 130 by a signal from source 132. Certain advantages may be inherent in certain applications with the modulation signal impressed on the photocathode to thereby modulate the primary electron beam. This embodiment provides still a further advantage in that the second modulating signal may be introduced directly to the dynode target member 122 and retarding potential filter 56 together if it would aid in the electron beam optics and image resolution. Finally, to compensate for slight deflection errors in the crossed field system due to the changing transit time it may be possible to apply the second input electrical correlation signal simultaneously to the anode electrodes biased at +V Adjustment may also be made between the modulation impressed on the photocathode, as well as that impressed on the combined dynode target member and retarding potential filter, to secure the desired operation in the intermediate crossover operating mode. The reflected secondary electron beam depicted by dashed line 62 is again finally collected by collector 36 as in FIG. 1.

Numerous alternatives may be employed for the scanning of the dynode target member 122. One embodiment may comprise the structure shown in FIGS. 6 and 7 with the scan beam readout on the same side as the photocathode. Alternatively, FIG. 9 illustrates a conventional scan type beam having two rear target meshes 134 and 136. The rear target meshes will be disposed within the retarding potential electrode region to assist in the operation in the intermediate crossover mode. During the correlation or writing cycle the first rear target mesh 136 will have a negative potential impressed from supply 138 while the other rear target mesh 134 is biased positively from supply 140. During the scan cycle both rear target meshes 134 and 136 will be switched to be grounded or have a slight positive potential.

FIG. 10 illustrates another capability of the scanning of the embodiment shown in FIG. 8 wherein the retarding potential filter 56 is isolated from target member 122 by insulator means 54. In this embodiment only one rear target mesh 142 is employed which is biased at a positive potential by voltage supply 144. During the correlation or writing cycle the retarding potential filter will be biased negatively by supply 146 and combine with the positive potential on the rear target mesh 144 to provide the electron image signals on the target member. During the scan cycle the retarding potential filter 56 is now biased positively as indicated by supply 148. Utilization of the foregoing scanning technique should be the simplest where conventional scanning from the rear of the dynode target member is desired.

Another alternative embodiment of the invention for the photocathode member is illustrated in FIG. 11. In this structure the sensitized photocathode surface may be provided over a portion of the overall cathode as, for example, the region denoted by the numeral 150. This portion of the overall cathode member is negatively biased by supply 152 as in the previously described embodiments. The lower half of the photocathode member is suitably metallized to provide a conductive coating 154 and is suitably isolated from the remainder of the photocathode by insulator 156. The metallized area serves as the collector for the reflected secondary electrons and is suitably biased by voltage supply 156.

There is thus disclosed an efficient image correlator device for electrooptical correlator systems. Numerous modifications, alterations and variations will readily occur to those skilled in the art without departing from the spirit and the scope of the invention as defined in the appended claims. It is intended, therefore, that the embodiment shown and described herein be considered as illustrative only and not in a limiting sense.

What is claimed is:

1. An image correlator device comprising:

an envelope having an electron image section dis posed at one end;

said envelope having a longitudinal axis;

said electron image section having a photoemissive cathode for converting electromagnetic energy signals into primary photoelectrons offset from said axis in one lateral direction;

a target member adapted to emit secondary electrons disposed in the path of said primary electrons adjacent to the opposing end of said electron image section and along the envelope axis;

means for separating and deflecting said primary and secondary electrons including means for providing crossed electric and magnetic fields disposed intermediate to said photocathode: and target member;

means for collecting said secondary electrons disposed on the same side as said photocathode and offset from said envelope axis in another lateral direction;

retarding potential electrical filter means for supporting and negatively biasing said target member to have a secondary electron emission ratio close to unity at a predetermined crossover operating mode;

means for biasing said crossed electric and magnetic fields to separate and deflect said electrons in a lateral direction; and

means for electronically scanning said target member to derive a correlated electrical output signal.

2. An electrooptical correlation system comprising:

means for directing electromagnetic energy signals in a beam to traverse a delay line modulator;

means for collecting said secondary electrons offset from the device axis in another lateral direction; crossed electric and magnetic field means for separating and deflecting said primary and secondary electrons disposed intermediate to said photoemissive cathode and target member;

means for biasing said crossed electric and magnetic field means to separate and deflect said electrons in a lateral direction;

retarding potential electrical filter means for supporting and negatively biasing said target member to have a secondary electron emission ratio close to unity at a predetermined crossover operating mode;

means for impressing a second modulating input electrical correlation signal on said electrical filter; and

means for electronically scanning said target member, collecting multiplying and integrating all electrical signals registered thereon to derive a correlated electrical output signal.

UNlTED STATES PATENT, OFFICE CERTIFICATE OF CORRECTION.

Patent 3,748,524 Dated July 24. 1973 lnventofls) John M, Osepchuk It is certified that error appears in the above-identified patent and that said Letters Patent arefhereby corrected as shown below:

Column 8, line 49-50 "rather than relying upon reflection" should read "upon. transmission of the- Column 9 line 8, after "biasing" insert -voltage supply 126 applies a positive voltage designated-.

Signed and sealed this 12th day'of March l974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents US COMM-DC 60376-P69 A U.5. GOVERNMENT PRINTING OFFICE: i959 0-365-33l 0 FORM PO-1050 (10-69) I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION.

Patent No. 3,748,524 Dated July 24. 1973 Inventor(s) John osepchukv It is certified that error appears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 8, line 49-50 "rather than relying upon reflection should read upon transmission of the-- Column 9 line 8, after "biasing" insert voltage supply 126 applies a positive voltage designated-.

Signed and sealed this 12th day of Maroh i974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents USCOMM-DC 603764 69 U.S. GOVERNMENT PRINTING OFFICE I9! 0-356-334 O ORM PO-I O50 (10-69) 

1. An image correlator device comprising: an envelope having an electron image section disposed at one end; said envelope having a longitudinal axis; said electron image section having a photoemissive cathode for converting electromagnetic energy signals into primary photoelectrons offset from said axis in one lateral direction; a target member adapted to emit secondary electrons disposed in the path of said primary electrons adjacent to the opposing end of said electron image section and along the envelope axis; means for separating and deflecting said primary and secondary electrons including means for providing crossed electric and magnetic fields disposed intermediate to said photocathode and target member; means for collecting said secondary electrons disposed on the same side as said photocathode and offset from said envelope axis in another lateral direction; retarding potential electrical filter means for supporting and negatively biasing said target member to have a secondary electron emission ratio close to unity at a predetermined crossover operating mode; means for biasing said crossed electric and magnetic fields to separate and deflect said electrons in a lateral direction; and means for electronically scanning said target member to derive a correlated electrical output signal.
 2. An electrooptical correlation system compriSing: means for directing electromagnetic energy signals in a beam to traverse a delay line modulator; said modulator having means for providing a first input electrical correlation signal to modulate the emergent signal beam pattern; photoelectric conversion and translation means for correlating said beam signals comprising: an image correlator device having a longitudinal axis and an electron image section including a photoemissive cathode for emitting a beam of primary photoelectrons offset from the device axis in one lateral direction; a target member adapted to emit secondary electrons disposed in the path of said primary electrons along the device axis; means for collecting said secondary electrons offset from the device axis in another lateral direction; crossed electric and magnetic field means for separating and deflecting said primary and secondary electrons disposed intermediate to said photoemissive cathode and target member; means for biasing said crossed electric and magnetic field means to separate and deflect said electrons in a lateral direction; retarding potential electrical filter means for supporting and negatively biasing said target member to have a secondary electron emission ratio close to unity at a predetermined crossover operating mode; means for impressing a second modulating input electrical correlation signal on said electrical filter; and means for electronically scanning said target member, collecting multiplying and integrating all electrical signals registered thereon to derive a correlated electrical output signal. 